The h Bar

0celo7

2:01 AM

those pants

Slereah

Well this was the 70's

0celo7

watched this a dozen times

Slereah

He's got a good delivery

0celo7

poontang :D

0celo7

2:16 AM

gtreat clip

Slereah

George Carlin - Suicide 2005 (Suicid)[RO SUB][uskro]

►

This one's pretty good too

0celo7

I've seen all of them

@ACuriousMind I'm not sure I understand this question

I don't think "all of it" is an answer you're looking for

ACuriousMind

Well, it's fine to be frustrated with the way physics works in general but I can't do anything about that.

Slereah

Maybe you can ask Jesus

0celo7

@ACuriousMind I'm not frustrated by the way physics works in general though

I'm frustrated by trying to make measurements in GR!!

Slereah

2:23 AM

Well

ACuriousMind

@0celo7 What about doing measurements in classical physics, or quantum mechanics? They all have their intricacies, too. I don't see what makes measurements in GR anything different.

Slereah

You can't measure an electric field either, you know

Not directly

0celo7

@ACuriousMind QM is strange and I've stopped caring about it

why bother since I don't know functional analysis, etc.

the structure of GR means that it is completely impossible to get anything close to good data

Slereah

Well in practice, the same thing apply to most measurements, really

The measuring apparatus always disturbs the system

ACuriousMind

The real world is just messy

0celo7

2:26 AM

but not to this degree

Slereah

Eh.

Gravity is pretty weak

Any error in measurement isn't gonna be huge

0celo7

I'm not even talking about disturbing the environment

I think you two are misunderstanding me

sure, measurements in QM change the system

sure, it's not possible to get anything really right in classical physics

Slereah

Well I know you're talking about measuring things at the same moment and all

But that's not really an issue either

Since the fields are continuous

0celo7

but in GR it is fundamentally impossible to even attempt to get info

Slereah

And usually slow changing

0celo7

2:28 AM

I'm not even talking about disturbing the system here

the mere attempt to get relevant data is impossible

Slereah

Is it

0celo7

yes!

Slereah

Well apparently that hasn't stopped people from doing it

ACuriousMind

@0celo7 No, you haven't seen that at all. You just realized that you can't figure out how to do it in a few hours. That's a big difference.

Slereah

Hey, have you ever read about algebraic QFT

It is somewhat related

0celo7

2:30 AM

@Slereah tried, gave up

not smart enough I'm afraid

Slereah

Measurements are done with a distribution on a section of space

There is no need to have the measurement of the field at the exact time $t$

You can just have it spread somewhat over time and space

No biggy

0celo7

@ACuriousMind but no one talks about it!!

that's freaky D:

ACuriousMind

@0celo7 No one you've read.

Slereah

Wait

Entropic gravity

Entropic gravity is a theory in modern physics that describes gravity as an entropic force—not a fundamental interaction mediated by a quantum field theory and a gauge particle (like photons for the electromagnetic force, and gluons for the strong nuclear force), but a probabilistic consequence of physical systems' tendency to increase their entropy. The proposal has been intensely contested in the physics community but it has also sparked a new line of research into thermodynamic properties of gravity. == Origin == The probabilistic description of gravity has a history that goes back at least...

0celo7

and then when someone like JD comes around telling us our books are too mathy

Slereah

2:32 AM

"Luboš Motl gives popular explanations of this problem in his blog."

Lubooooos

0celo7

we just laugh at him

but he's right!

@ACuriousMind To be fair I have read the standard texts.

Slereah

Well, our books, yes

ACuriousMind

@0celo7 No, we do not laugh at him because he says we might be a little too insistent on math

Slereah

But not all books are such with GR

ACuriousMind

@0celo7 Yeah. What reason would a standard text about the theory have to discuss the experimental realizations. Which mechanics book talks about how to measure fast moving particles, or oscillations in a supercooled circuit, or whatever? Which electrodynamics book talks about proper antenna design?

0celo7

2:34 AM

@ACuriousMind Good ones!

Slereah

I think you mean

BOOKS FOR ENGINEERS

The thing is, in actual experimental settings

You don't really need GR

Real life situations are way too faint

Almost everything can be done with linearized gravity

ACuriousMind

@0celo7 No. Because every experimental setting is different. You just can't be general enough to write a book about it. There's gonna be a series of papers for every specific setup, where a group of people thought long and hard about how to actually construct the experiment.

Slereah

Tho do see the paper I linked

Well, there aren't that many GR experiments, either

I mean at its core, there's like... 6 or 7 really different experiments?

0celo7

@ACuriousMind but there should be some general method

sure, it has to be specialized

ACuriousMind

That's what experimentalists do - construct experiments. If there were standard books telling us how to do that, we wouldn't need so many of them

0celo7

2:37 AM

but there are certainly some guidelines

ACuriousMind

@0celo7 That's just an assertion because you want the world to be simpler than it actually is.

Slereah

Perihelion of mercury, time dilatation in a potential, bending of light, detection of gravitational waves, change of orbiting twin systems, lens thirring precession

Hm, what else

0celo7

gravity probe B

or is that precession

Slereah

Well gravity probe B had precession and a few others

Oh, the speed of gravity thing

0celo7

frame tearing, right?

speed of gravity?

ACuriousMind

2:39 AM

Have you done a physics lab? I think you might have a very idealized view of what experimenting is because you've never done it.

Slereah

Ah, the speed of gravity thing didn't work out

0celo7

@ACuriousMind uh, I work in one?

I've been to the Oak Ridge neutron beam line

ACuriousMind

@0celo7 What do you do?

0celo7

@ACuriousMind try to figure out how much has been done on ion tracks in carbonates

ACuriousMind

Yeah, that's not what I mean

0celo7

2:40 AM

reading literature at the moment

ACuriousMind

I mean actually doing an experiment. Seeing how fiddly the dials are and how noisy the signals. How far off you can be from the theoretical prediction. How the data you collect doesn't have much to do, at first sight, with the thing you want to measure and requires fitting and extrapolating.

0celo7

Dude, I'm not asking the books to describe that much detail

But how do I got about looking at something through my telescope 1000000 light years away

and how to I know if that data can be used for numerical GR

or if the geometry is rapidly fluctuating

ACuriousMind

@0celo7 But those details are precisely what the experiments are about!

0celo7

or how do coordinate systems work

@ACuriousMind I'm not asking for that then!!

Slereah

@0celo7 : I think you'd better look at actual GR experiments

Instead of making them up in your mind

They're not all that complicated

0celo7

2:45 AM

@Slereah That's the problem

I want 3 black holes fucking

That kind of craziness

How would one set up and experiment there?

Slereah

Well yeah, but we have 0 black holes around

0celo7

EXACTLY

Slereah

Well we can't do much about that

0celo7

3 black holes a billion light years away

ACuriousMind

So...you're upset that no one spends effort on describing experiments we won't actually ever be able to perform?

0celo7

2:49 AM

@ACuriousMind YES

Now you're making me sound like some crazy person

ACuriousMind

Well, we can't do anything about people not being willing to waste their time :P

0celo7

@ACuriousMind Oh like that's any bigger of a waste than infinity topoi

ACuriousMind

@0celo7 Yes, it is. Math is not meant to describe anything "real", to be performed or applicable. But the only value of experiments lies in performing them, and if you know you can't, why bother?

0celo7

@ACuriousMind I was referring specifically to infinity topoi in physics

to me that has just as much value was a hypothetical black hole threesome

ACuriousMind

@0celo7 There are very few people who do that, and their goal is to provide a better mathematical framework for understanding what the essence of a theory is, not to actually do concrete physics.

0celo7

2:53 AM

if anything for the value of understanding the structure of GR better

ACuriousMind

There's no such abstract goal for experiments. They are there to measure stuff. If they can't, they don't do anything.

0celo7

@ACuriousMind but by measuring things we can understand the theory better

ACuriousMind

@0celo7 How?

0celo7

and proposing how to measure things

@ACuriousMind because we learn how to inpterpret data

and the black hole threesome is not trivial to interpret as far as I can see

ACuriousMind

@0celo7 if we actually get that data. But if we know we won't ever get that data because there just is not weird warped spacetime around, what's the point?

0celo7

2:54 AM

there's a lot of interesting things to consider

curvature from here to there

fucked up curvature there

time that light takes to travel

@ACuriousMind just considering it has immense value!

I'm really astonished that you of all people are arguing against a theoretical investigation of something on principle

ACuriousMind

@0celo7 Because it's not a theoretical investigation you apparently want.

And I'm not against it

0celo7

@ACuriousMind of course it is

ACuriousMind

I just don't see any reason to do it.

0celo7

@ACuriousMind to understand how one would do the measurement

this tells us about the structure of the theory

ACuriousMind

@0celo7 But we won't ever be in that situation. What do you gain from knowing how to perform an experiment without doing it?

0celo7

2:59 AM

@ACuriousMind STRUCTURE OF THE THEORY

ACuriousMind

Give me one example.

0celo7

and you don't know that

@ACuriousMind what is wrong with the black hole threesome in a fucked up inflating, fluctuating universe

ACuriousMind

Just one instance where knowing how you would, in some contrived situation, measure something, tells you something about the theory

@0celo7 Yeah, so what would you gain if you knew how to measure spacelike geodesics length in arbitrary situations?

0celo7

@ACuriousMind it would tell me how coordinates work, how light behaves over very long distances, how mesurements of curvature work over very long distances

about time dilation across such large distances

how the expanding and flucating of spacetime affects light rays

how gravitational waves disturb our measurements

ACuriousMind

@0celo7 They follow light-like geodesics. What has the measurement to do with that?

0celo7

3:01 AM

@ACuriousMind how are null geodesics affected by g waves and expansion and all this other crap

but whatever, I'm just another nut

ACuriousMind

@0celo7 What has the measurement to do with that? Everything you say there can be investigated in the theory without knowing how to measure anything

0celo7

@ACuriousMind because I would also like to know how to measure this stuff!

ACuriousMind

@0celo7 So...the value of knowing how to measure things lies in you wanting to know how to measure things? I'm not convinced.

0celo7

@ACuriousMind oh like that's any crazier than infinity topoi

Slereah

Null geodesics being affected by g waves will be reflected by light deviation and redshifting

0celo7

3:04 AM

I thought people just like to know things

why are you saying pursuit of knowledge is a waste of time

I'm very confused

ACuriousMind

@0celo7 Not saying that! If you, personally want to know this, go for it. But you're acting as if other people should have investigated this, and you fail to give any reason for that.

For yourself, "wanting to know" is a perfectly fine motivation. But faulting others for not wanting to know the same is unreasonable.

0celo7

@ACuriousMind nah, I wouldn't go for it

@ACuriousMind I'm just shocked

@ChrisWhite does literature on this exist?

0celo7

3:20 AM

@ACuriousMind I'm shocked that none of the standard texts even really attempt one scenario

maybe MTW does, @Slereah

@ACuriousMind and now you probably think I'm a nut and wonder where this is coming from

in ODE class we discussed inverse square motion as the canonical example of coupled ODEs

so ofc my next thought was the Cauchy problem in GR

and Freire showed how one gets the geometric parameters from some simple mesurements one can make with a telescope

so ofc my question is how can I determine the metric of spacetime with a telescope

Slereah

MTW has some experimental stuff I think, yeha

0celo7

@ACuriousMind this seems like a perfectly natural question...

Slereah

@0celo7 : Do you know the

OPTICS APPROXIMATION

Or whatever it's called

0celo7

Eikonal?

Slereah

I forget

It's the thing where you treat objects in GR like lenses

0celo7

3:23 AM

hmm

no

ACuriousMind

@0celo7 Ah, the thing where they show you one of the pretty examples and you think it should work that way without approximations for more complicated things.

0celo7

@ACuriousMind you make me sound like a child

ACuriousMind

As we said, you have to do approximations. Like supposing the spatial geometry doesn't change fast. Or linearized gravity. Or whatever.

0celo7

well I want to know what the best we can do without making approximations is

ACuriousMind

@0celo7 Inexpericenced, I'd say. Why do you think people love the harmonic oscillator so much? Because it's the one approximation you always do if you want to get anything done.

Not doing approximations is hard, and not seen as worth the trouble if the experiments devised with the approximated framework give good results.

So, I still think your insistence on people doing this in "full GR" comes from you not realizing how often people do approximations when going away from the pure theory to actually measureing and observing things.

Slereah

3:28 AM

If you want to do full GR you do numerical GR

although you'll still do approximations

0celo7

hmm

Slereah

For instance, if you model dark matter by gravitational lensing

You will do it in the test field limit

0celo7

I might be destined to a math thesis on numerical methods

in GR

wonder if that would fly

Slereah

The light that passes through doesn't contribute to the gravitational field

0celo7

I don't really care about that

I accept that there should be an approximation there

> When bicycle and motorcycle riders "pop a wheelie," a large acceleration causes the bike's front wheel to leave the ground. Let M be the total mass of the bike-plus-rider system; let x and y be the horizontal and vertical distance of this system's cm from the rear wheel's point of contact with the ground.

Problem is to determine the minimum acceleration to lift the front wheel

I have...absolutely no idea where to begin

Slereah

3:35 AM

Do an experiment

Pop a wheelie

0celo7

I did

got approximately $xg/y$

NeuroFuzzy

4:17 AM

@0celo7 At rest there is a downward force on the front wheel. (so find it). In an accelerating frame there is a force on the CM (find it), so a torque (find it), so an upwards force on the wheel (find it).

0celo7

@NeuroFuzzy what is the normal force on the front wheel vs. rear wheel

NeuroFuzzy

At rest? You can find it by looking at torques.

orrrr a balance beam

0celo7

@NeuroFuzzy huh?

the torques on the CM?

NeuroFuzzy

@0celo7 It's a balance beam at the two wheels with the CM placed on it. You can find the force needed to support two ends of a balance beam.

0celo7

@NeuroFuzzy I don't know what that means

NeuroFuzzy

4:24 AM

@0celo7 A... a lever? A beam with a mass on it. A massless rod with a weight placed somewhere in its middle.

Thus ceases the hints! I'm doing more work for my midterm hehe

0celo7

@NeuroFuzzy Yeah, so?

NeuroFuzzy

can't procrastinate too much.

@0celo7 so that gives you the forces on both wheels when the motorcycle is at rest

0celo7

@NeuroFuzzy I still don't see why that's important...

NeuroFuzzy

and once that's done you can go into an accelerating frame and add in the fictitious forces caused by that, and then look at the upwards force on the front wheel and there's your answer.

0celo7

wait, don't go!

one more thing

@NeuroFuzzyhttps://gyazo.com/3d37ddb1574a679e8680866e87131bee

assuming the spring is unstretched at $\theta = 30$

then is the work on the falling rod due to the spring $-\int kL^2\sin\theta(\sin\theta-\tfrac{1}{2})\mathrm{d}\theta$

$kL(\sin\theta-1/2)$ is the force on the rod from the spring

then multiply by $L\sin\theta$ and integrate

gyazo.com/3d37ddb1574a679e8680866e87131bee

and somehow the work is positive

wait a moment

I might be stupid

user54412

5:05 AM

@0celo7 Black Hole Triple Dynamics: A Breakdown of the Orbit Average Approximation and Implications for Gravitational Wave Detections

0celo7

@ChrisWhite interesting

will look at

not now

struggling with mechancis

user54412

I can't guarantee it's even worth looking at. Just pointing out that it exists.

0celo7

@ChrisWhite I need a worldly person

is 27ft/s^2 a lot of acceleration

for a motorcycle

user54412

isn't that almost 1 g

0celo7

yes

user54412

5:13 AM

for more than a split second it would be rather difficult to hold on I would imagine

user54412

then again, I'm not worldly enough to have ever driven a motorcycle

0celo7

I'm trying to lift the front wheel off of the ground

user54412

because the center of mass is above the center of thrust?

0celo7

ya

wow I calculated the static friction between the rear wheel and the road as .85

is that reasonable?

user54412

uh sure?

0celo7

5:17 AM

for the rear wheel I just got $\Sigma F_x=f=ma$ and $\Sigma F_y=N-mg=0$

and using $f=\mu_s N$ I get the standard $\mu_s=a/g$

user54412

not entirely sure why static friction is involved

user54412

also not sure if \Sigma is supposed to be \Sum

0celo7

@ChrisWhite to see what $\mu_s$ is needed for the rear wheel to not slip during this maneuver

@ChrisWhite it's a sum, yes

user54412

@0celo7 oh. well that's just a limitation of driving a non-awesome motorcycle (where awesome = jet-powered)

0celo7

did you get Fallout4?

user54412

5:19 AM

i haven't gotten around to playing 1-3, so no

0celo7

me neither

but I got 4

it's goooooood

65mph

have to convert that into fps

how many feet in a mile

5280?

user54412

@0celo7 it's like you grew up in Germany or something :p

0celo7

@ChrisWhite nah

I couldn't do the equivalent for whatever they use

I grew up bad with both systems

user54412

so today I learned that with certain international space collaborations, the Germans will use one lat/long coordinate system for a planet and the French will use another

0celo7

good

argh this problem has too much trig

why is everything so hard

wait, do the normal forces even point up

@ChrisWhite do the normal forces on the tires point straight up?

user54412

5:29 AM

the point... normal to the surface, right?

0celo7

well

maybe

perhaps there's some GR effect going on and "normal" is ambiguous

classical mechanics on curved spacetime

aha

@ChrisWhite good news, it's 90 degrees to the surface

AHA

NOT ONLY IS IT 90 DEGREES

but the torque around the CM is zero

oh great now there's a horrible system of equations

fml

yassss

calculator thank you

user116211

5:48 AM

@DanielSank: He is back again with his non-sense speculations. Here is his another answer: physics.stackexchange.com/a/219113/36790 & here his new account: physics.stackexchange.com/users/98850/peteravr

0celo7

it's funny because a real stalker would look up the real dmckee and the real dan Sank

and find where they work

and then get various infos

and confirm they are separate people

honestly he's a pretty shitty stalker

user116211

@Ocelo7: I betcha he is a **** psychopath.

0celo7

@user36790 not a very good one

I'm not even that bad and I could show him some tricks

user116211

Actually he has crossed every limits; really I wanna kill him now.

0celo7

o.o what the hell

calm down

get help if you're srs about that

see, if he were really good

he's find DS or dmckee online

not too hard to find out where they work

and then ambush

user116211

5:57 AM

His funny & nonsensical allegations: Mods get money for their work; DanielSank & dmckee are the same men (wtf!!) ; Danielsank runs the site (call NYPD) ; Danielsank knows no physics (send him to Auswitz); blah, blah, blah..... I think he is from ISIS :P

0celo7

NYPD, Auschwitz and ISIS in the same sentence

user116211

I was watching Quantico:P

0celo7

in any case, not a psychopath

just some angry kid

if we don't hear from either Dan or David in a few days...we might have to worry

although, he seems to have it out for Dan

but if I were him I would take out both, just to be sure

user116211

Well yesterday I asked DavidZ for this menace; he checked & removed that answer; but he seems to quite adamant with DanielSank!

user116211

Really?

0celo7

6:03 AM

@user36790 really what?

user116211

No, if you were him, what would be your tricks to take down Daniel?

0celo7

dunno

would have to scope out the area first

the years of Hitman, Splinter Cell and Metal Gear games would come in handy

user116211

Have you watched the Hitman movie ?

0celo7

no

user116211

Hmmm... so, have you played the latest Assassins Creed ; I 've forgotten to count the number:/

0celo7

6:07 AM

@user36790 add that on there too

I played 1, 2, Revelations and a bunch of mobile ones

I'll get some more ACs when they're on sale

I wonder how big @dmckee is

that would ofc influence the strategy

and we know that he is married

user116211

It's my favourite franchise; I completed AC 3; thanks to Amazon. But they are really making it difficult as they are releasing 2-3 series at a single year:(

0celo7

it's a cash cow franchise

the Ubisoft currency printing press

in any case, that's it for Agent Ocelot

wouldn't want David or Dan thinking I'm nuts or something

good night

user116211

Oh! my **** that stalker or the psycho got one upvote!!!! I think he voted his answer from another account:/

user116211

Yes, sweet dreams:)

0celo7

oh my [4 letter expletive]

can't think of what that would be

lord?

user116211

6:14 AM

I also don't know what would be there? But every GOOD words come in 4 letters:P

0celo7

ah!

it must be "fart"

user116211

Nice one !

yuggib

7:54 AM

the (european) morning desert that is called the $\hbar$ chat...

DanielSank

@user36790 Would you mind not talking about that user any more?

I am disturbed by what's going on here and I'd ask that you simply ignore that user.

skill patrol

8:55 AM

A disturbing troll indeed.

Time to call the Troll Hunter ;-)

DanielSank

10:23 AM

Low-background steel

Low-background steel is any steel produced prior to the detonation of the first atomic bombs in the 1940s and 1950s. With the Trinity test and the Atomic bombing of Hiroshima and Nagasaki in 1945, and then subsequent nuclear weapons testing during the early years of the Cold War, background radiation levels increased across the world. Modern steel is contaminated with radionuclides because its production used atmospheric air. Low background steel is so-called because it does not suffer from such nuclear contamination. This steel is used in devices that require the highest sensitivity for detecting...

yuggib

11:43 AM

1

Q: How $\pi$ is derived from quantum mechanics

I came across this article New Derivation of Pi Links Quantum Physics and Pure Math in which they discuss about a recent discovery of deriving PI from physics. I am not a physicist or a mathematician and able to grasp only a little. Can you explain the discovery and its significance for a simplet...

derive $\pi$...classic but always hilarious

Slereah

What's the uncertainty on $\pi$

$\delta pi \delta e \geq \frac{\hbar}{2}$

yuggib

:-D

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